1. Field of the Invention
The present invention relates to a mobile communication system in which radio communication is performed between a ground radio base station and a subscriber station (for example, a fixed radio station, a semi-fixed radio station, a mobile station, a portable radio station and so on) by using a Time Division Multiple Access (TDMA) method, a Code Division Multiple Access/Time Division Duplex (CDMA/TDD) method or a Time Divided CDMA method.
2. Description of Related Art
In a mobile communication system, communication of information is, for example, performed between a mobile station such as a mobile on-vehicle communication apparatus or a mobile portable communication apparatus and a ground radio base station through a radio channel.
A technique, in which a satellite is added to the mobile communication system to make the satellite function as a relay repeater, has been disclosed in the patent gazette: Publication of the Japanese Application No. H7-75344 of 1995, the Published Unexamined Japanese Patent Application No. S58-131842 of 1983, the Published Unexamined Japanese Patent Application No. S59-6642 of 1984 and the Published Unexamined Japanese Patent Application No. H5-130001 of 1993.
However, the satellite functions only as a relay repeater, but the satellite has no function for adjusting the phase of a radio wave transmitted and received.
Because the conventional mobile communication system has the above described configuration, a satellite can be used as a relay repeater. However, because the satellite has no function for adjusting a phase of radio wave, a phase shift between a radio wave directly transmitted from a ground radio base station and a radio wave transmitted from the ground radio base station through the satellite is generated in a subscriber station. Therefore, even though a power of one of the radio waves is weakened, there is a problem that it is difficult to hand over the other radio wave to the subscriber station.
The present invention is provided to solve the above problems, and has an object of providing a mobile communication system which can be used in cases where the radio waves are received in a subscriber station. At the same time, the present invention allows while changing over from either one of a radio wave directly transmitted from a ground radio base station and a radio wave transmitted from the ground radio base station through a satellite (a stratospheric platform base station) to the other in response to conditions of the radio waves.
In a mobile communication system according to the present invention, when a prescribed delay time passes after the transmission of a radio wave to a stratospheric platform base station, another radio wave relating to the same information as that indicated by the radio wave is transmitted to a subscriber station.
Therefore, a phase of a radio wave directly transmitted from a ground radio base station can be synchronized with a phase of a radio wave transmitted from the ground radio base station through the stratospheric platform base station. Accordingly, when one of the radio waves becomes weakened, it is possible to hand over the other radio wave to the subscriber station.
In a mobile communication system according to the present invention, the subscriber station compares a phase of the radio wave transmitted from the ground radio base station with a phase of the radio wave transmitted from the stratospheric platform base station, the subscriber station transmits phase difference information, the ground radio base station receives the phase difference information from the subscriber station, and the ground radio base station adjusts the prescribed delay time.
Therefore, the phase synchronization can be precisely performed, and communication turbulence in a hand-over operation can be suppressed.
In a mobile communication system according to the present invention, the subscriber station has a plurality of phase detectors for respectively detecting phase difference information and transmits the pieces of phase difference information to a plurality of ground radio base stations.
Therefore, even though the subscriber station moves to a zone of an adjacent ground radio base station during the communication, communication turbulence can be suppressed.
In a mobile communication system according to the present invention, the subscriber station transmits the phase difference information in which one symbol length is a minimum unit.
Therefore, the phase synchronization can be performed more minutely.
In a mobile communication system according to the present invention, the subscriber station transmits the phase difference information in which one chip rate length is a minimum unit.
Therefore, the phase synchronization can be performed more minutely.
In a mobile communication system according to the present invention, the ground radio base station compares a phase of the radio wave transmitted from the stratospheric platform base station with a phase of the radio wave transmitted to the subscriber station and adjusts the prescribed delay time according to a comparison result.
Therefore, the phase synchronization can be precisely performed, and communication turbulence in a hand-over operation can be suppressed.
Also, the phase synchronization can be performed more minutely.
In a mobile communication system according to the present invention, the ground radio base station adjusts the prescribed delay time according to the comparison result in which one symbol length is a minimum unit.
Therefore, the phase synchronization can be performed more minutely.
In a mobile communication system according to the present invention, the ground radio base station adjusts the prescribed delay time according to the comparison result in which one chip rate length is a minimum unit.
Therefore, the phase synchronization can be performed more minutely.
In a mobile communication system according to the present invention, the stratospheric platform base station receives the radio wave transmitted from the ground radio base station, measures a frame length of the radio wave, compares the frame length with a standard frame length and adjusts a delay time extending from the reception of the radio wave to the transferring of the radio wave according to a comparison result.
Therefore, even though the stratospheric platform base station is moved by an air flow, phase synchronization can be performed.
In a mobile communication system according to the present invention, the stratospheric platform base station receives the radio wave transmitted from the ground radio base station, measures a multi-frame length of the radio wave, compares the multi-frame length with a standard multi-frame length and adjusts a delay time extending from the reception of the radio wave to the transferring of the radio wave according to a comparison result.
Therefore, even though the stratospheric platform base station is moved by an air flow, phase synchronization can be performed.
In a mobile communication system according to the present invention, the stratospheric platform base station receives the radio wave transmitted from the ground radio base station, measures a super-frame length of the radio wave, compares the super-frame length with a standard super-frame length and adjusts a delay time extending from the reception of the radio wave to the transferring of the radio wave according to a comparison result.
Therefore, even though the stratospheric platform base station is moved by an air flow, phase synchronization can be performed.
In a mobile communication system according to the present invention, the stratospheric platform base station adjusts a delay time for each of radio waves transmitted from a plurality of ground radio base stations in cases where link channels are set between the stratospheric platform base station and the plurality of ground radio base stations.
Therefore, even though one link channel is disconnected by an accident or natural conditions, a lack of information can be prevented.
In a mobile communication system according to the present invention, the stratospheric platform base station receives a plurality of radio waves transmitted from a plurality of ground radio base stations, the stratospheric platform base station selects one of the radio waves, and the stratospheric platform base station transfers the selected radio wave to the subscriber station.
Therefore, the radio wave received under superior conditions can be transferred to the subscriber station.
In a mobile communication system according to the present invention, TDMA signals and time divided CDMA signals are included in time slots composing a frame to construct the information to be transmitted.
Therefore, a large number of pieces of high-speed data and pieces of low-speed data can be simultaneously transferred.
In a mobile communication system according to the present invention, one or more TDMA signals and one or more time divided CDMA signals are included in time slots, which are successively transferred along a time axis and are selected from a plurality of time slots composing a frame, to construct the information to be transmitted.
Therefore, a large number of pieces of high-speed data and pieces of low-speed data can be simultaneously transferred.